Intersubband Absorption Linewidth Research Articles

Combined influences of temperature, pressure, and alloy-composition on magneto-optical properties of the semi-parabolic well under all four different phonon models

In this study, combined influences of the pressure, alloy composition, and temperature on the magneto-optical properties of the semiparabolic well under all four different phonon models, including three confining phonon models are considered in detail through the magneto-phonon resonance oscillation (MPRO). The magneto-optical transport absorption power (MOTAP) and MO-conductivity tensor (MOCT) expressions are obtained utilizing the method of operator projection. Simultaneously the profile method also is used in order to measure the inter-subband absorption linewidth. Our calculated result shows that (i) the aluminum composition y has significant effect on the position of the resonant peak; (ii) the absorption line-width as a function of the Al-composition, temperature of electron, and hydrostatic pressure for all four models of phonons; (iii) the influence of the Al-composition, temperature of electron, and pressure on the intersubband absorption line-width is different for each of phonon model; (iv) our present result is fairly consistent with experimental measurement; (v) combined effects of the aluminum composition, the temperature of electron, and the hydrostatic pressure on the intersubband absorption line-width of the semiparabolic QWs are important when the phonon confinement is taken into consideration.

Intersubband absorption linewidth in a semi-parabolic quantum well: Comparison among three different phonon models

In this article, effects of different confined phonon models on intersubband absorption linewidth in semiparabolic quantum well (SPQW) is studied in detail through considering the optically detected magneto-confined phonon resonance (ODMCPR) effect. The projection operator and profile methods are utilized in order to calculate the linear conductivity tensor as well as magneto-phonon resonance absorption power (MPRAP) and measure the absorption linewidth or the full width at half maximum (FWHM) at the ODMCPR peak, respectively. We find that (i) the FWHM (absorption linewidth) as functions of the temperature, Landau level, and confining potential frequency; (ii) there is a different dependence in slab and guided phonon modes, as well as Huang–Zhu (HZ) phonon mode model on the FWHM; (iii) the confined phonon modes have great influence on the intersubband absorption linewidth in semiparabolic quantum well; (iv) the present calculations accord well with previous experimental studies.

Structural and optical properties of nonpolar m- and a-plane GaN/AlGaN heterostructures for narrow-linewidth mid-infrared intersubband transitions

Mid-infrared intersubband transitions are investigated in nonpolar m-plane and a-plane GaN/AlGaN multi-quantum well heterostructures. Nominally identical heterostructures were grown by ammonia molecular-beam epitaxy on free-standing m-plane and a-plane GaN substrates. A total of 12 well- and barrier-doped samples with intersubband transition energies in the range of 220–320 meV (wavelength range 3.8–5.6 μm) were grown. The intersubband absorption lines of the m-plane samples were 10–40% narrower than those of the a-plane samples, and a very narrow intersubband absorption linewidth of 38 meV (full width at half maximum) at a transition energy of approximately 250 meV (5 μm wavelength) was observed in an m-plane sample. Narrower intersubband absorption linewidths of m-plane samples can be explained by more abrupt heterostructure interfaces revealed by structural characterization, which is attributed to a higher stability of the m-plane compared to the a-plane. No significant difference in the intersubband absorption linewidth was observed between the barrier- and well-doped samples.

Intersubband optical absorption in GaAs parabolic quantum well due to scattering by ionized impurity centers, acoustical and optical phonons

The intersubband absorption linewidth dependence on well width in GaAs quantum well is calculated. Three mechanisms of scattering have been discussed there: carriers scattering by optical (LO), acoustic (LA) phonons and ionized impurity centers (ION). The method which used for calculations is similar to a well-known method of calculating transport mobility. The estimation for absorption coefficient is proposed, based on two-dimensional dynamical conductivity expression. The LO phonon emission process is activated starting from some quantum well (QW) width so it has its impact on absorption linewidth.

Intersubband absorption due to scattering on ionized impurities and acoustic phonons in parabolic quantum well

Intersubband absorption linewidth in GaAs quantum well due to scattering by LA phonons and ionized impurities is calculated. The method which used for calculations is similar to a well-known method for calculating transport mobility. The linewidth dependence on temperature, as well as on well width is presented. The estimation for absorption coefficient is proposed, based on two-dimensional dynamical conductivity expression. The coefficient is calculated for different well widths, as well as for different temperatures.

A novel approach to the evaluation of the interface roughness scattering form factor in intersubband transitions

We propose a modification of the interface roughness (IFR) scattering form factor in intersubband transitions. We properly derived a formula for the form factor for IFR scattering in terms of the integrals of the envelope wave functions. This new form factor has a more global natural than the old one (proposed by Ando) and may be suitable for a wide range of applications. In this paper, we calculate and compare the absorption linewidths by applying of the old form factor and the new one. Different from previous calculations, for the same surface profile (Δ, Λ), the interface roughness scattering absorption linewidth calculated with the new form factor is twice as great as that calculated with the old one. Our numerical calculations may better explain the experimental results for the well-width dependence of the intersubband absorption linewidth.

Improvement of near-infrared absorption linewidth in AlGaN/GaN superlattices by optimization of delta-doping location

We report a systematic study of the near-infrared intersubband absorption in AlGaN/GaN superlattices grown by plasma-assisted molecular-beam epitaxy as a function of Si-doping profile with and without δ-doping. The transition energies are in agreement with theoretical calculations including many-body effects. A dramatic reduction of the intersubband absorption linewidth is observed when the δ-doping is placed at the end of the quantum well. This reduction is attributed to the improvement of interface roughness. The linewidth dependence on interface roughness is well reproduced by a model that considers the distribution of well widths measured with transmission electron microscopy.

Single-valued estimation of the interface profile from intersubband absorption linewidth data

We study the ratio between different linewidths of the intersubband absorption in a quantum well. For roughness-related absorption, this ratio turns out to be independent of the roughness amplitude, so being a function of the correlation length only. Therefore, in contrast to the earlier belief, we may propose an efficient method for individual single-valued estimation of the two sizes of an interface profile from optical data. Instead of the simultaneous fitting of both sizes to the functional dependence of the linewidth at many experimental points, we perform a two-step fitting of (i) correlation length to the linewidth ratio at one point and then (ii) roughness amplitude to a linewidth at one point. This method is useful for experimental study of the interface morphology.

Macroscopic defects in GaN/AlN multiple quantum well structures grown by MBE on GaN templates

We have used MBE to grow in AlN/GaN superlattices, with different number of periods, on 2.5-μm-thick MOVPE-GaN templates to study the development of defects such as surface deformation due to strain. After growth the samples were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), XRD and Fourier transform infrared spectroscopy (FT-IR). The strain increased with the number of quantum wells (QWs) and eventually caused defects such as microcracks visible by optical microscopy at four or more QW periods. High-resolution TEM images showed shallow recessions on the surface (surface deformation) indicating formation of microcracks in the MQW region. The measured intersubband (IS) absorption linewidth from a four period structure was 97meV, which is comparable with the spectrum from a 10 period structure at an absorption energy of ∼700meV. This indicates that the interface quality of the MQW is not substantially affected by the presence of cracks.

Electroabsorption Modulator Using Intersubband Transitions in GaN–AlGaN–AlN Step Quantum Wells

We calculate the high-speed modulation properties of an electroabsorption modulator for lambda=1.55 mum based on Stark shifting an intersubband resonance in GaN-AlGaN-AlN step quantum wells. In a realistic simulation assuming an absorption linewidth Gamma=100 meV we obtain an RC-limited electrical f3dB~60 GHz at an applied voltage swing Vpp=2.8 V. We also show that a small negative effective chirp parameter suitable for standard single-mode fiber is obtained and that the absorption is virtually unsaturable. The waveguide is proposed to be based on the plasma effect in order to simultaneously achieve a strong confinement of the optical mode, a low series resistance, and lattice-matched cladding and core waveguide layers. Extrapolated results reflecting the decisive dependence of the high-speed performance on the intersubband absorption linewidth Gamma are also given. At the assumed linewidth the modulation speed versus signal power ratio is on a par with existing lumped interband modulators based on the quantum confined Stark effect

Investigation of the design parameters of AlN/GaN multiple quantum wells grown by molecular beam epitaxy for intersubband absorption

AlN/GaN multiple quantum wells were grown by RF plasma-assisted molecular beam epitaxy on (0 0 0 1) sapphire substrates. Intersubband (ISB) absorption in the range of 1.5–1.9 μm was investigated in these structures as a function of the main quantum well design parameters. It is found that the ISB transition line width does not depend strongly on the degree of strain relaxation in the investigated structures, but rather is sensitive to both the well and barrier widths. This is explained by considering well/barrier thickness fluctuations. A reduction in the ISB absorption line width was achieved by doping the wells in the first 5 Å only as compared to uniformly doping the wells. ISB absorption was also demonstrated for the case in which the AlN barriers only were doped.

Linewidth for interconduction subband transition in Si/Si1−xGex quantum wells

AbstractThe intersubband absorption linewidth has much importance in the operation of quantum well infrared photodetectors (QWIPs) and quantum cascade lasers (QCLs). Here we calculate the intersubband absorption linewidth due to interface roughness scattering, deformation potential acoustic phonon scattering, and optical (intervalley) phonon scattering via the deformation potential, i.e. g phonon. We consider the n‐type Si/Si1−xGex structure. The linewidths are studied for various well widths and different in‐plane kinetic energy. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Intersubband absorption linewidth in GaAs quantum wells due to scattering by interface roughness, phonons, alloy disorder, and impurities

We calculate the intersubband absorption linewidth 2Γop in quantum wells (QWs) due to scattering by interface roughness, LO phonons, LA phonons, alloy disorder, and ionized impurities, and compare it with the transport energy broadening 2Γtr=2ℏ/τtr, which corresponds to the transport relaxation time τtr related to the electron mobility μ. Numerical calculations for GaAs QWs clarify the different contributions of each individual scattering mechanism to the absorption linewidth 2Γop and transport broadening 2Γtr. Interface roughness scattering contributes about an order of magnitude more to the linewidth 2Γop than to the transport broadening 2Γtr, because the contribution from the intrasubband scattering in the first excited subband is much larger than that in the ground subband. On the other hand, LO phonon scattering (at room temperature) and ionized impurity scattering contribute much less to the linewidth 2Γop than to the transport broadening 2Γtr. LA phonon scattering makes comparable contributions to the linewidth 2Γop and transport broadening 2Γtr, and so does alloy disorder scattering. The combination of these contributions with significantly different characteristics makes the absolute values of the linewidth 2Γop and transport broadening 2Γtr very different, and leads to the apparent lack of correlation between them when a parameter, such as temperature or alloy composition, is changed. Our numerical calculations can quantitatively explain the previously reported experimental results.

Effects of interface roughness and phonon scattering on intersubband absorption linewidth in a GaAs quantum well

We experimentally and theoretically study the effects of interface roughness and phonon scattering on intersubband absorption linewidth in a modulation-doped GaAs/AlAs quantum well. Quantitative comparisons between experimental results and theoretical calculations make it clear that interface roughness scattering is the dominant scattering mechanism for absorption linewidth in the temperature range below 300 K. Even at room temperature, phonon scattering processes contribute little to linewidth, while polar-optical phonon scattering limits electron mobility.

Interface roughness and alloy-disorder scattering contributions to intersubband transition linewidths

We report measurements of intersubband absorption in single semiconductor quantum wells of different well widths and alloy compositions. The well width dependence of the intersubband absorption linewidth is consistent with broadening dominated by interface roughness. The linewidth, however, is found to be relatively unaffected by alloy composition in the quantum well, making alloying an effective tool in the design of quantum well optical devices relying on intersubband transitions.